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Thursday, December 15, 2011

Comet C/2011 W3 (Lovejoy) approaches the Sun

Australian amateur astronomer Terry Lovejoy discovered on Nov. 27.7 his third comet, designated C/2011 W3 (Lovejoy). On our previous post about this comet you can see our follow-up image and animation.

C/2011 W3 is a Kreutz sungrazer, a family of sungrazing comets that are named after German astronomer Heinrich Kreutz who first studied them in the details. These comet fragments passes extremely close to the Sun at perihelion and usually they completely evaporated during such a close approach.

Many Kreutz sungrazer comets are observed each year by SOHO Sun-observing satellite. SOHO provides a constant view of the immediate solar vicinity and it has now discovered more than 2000 of new sungrazing comets, some just a few metres across. About 83% of the sungrazers found by SOHO are members of the Kreutz group, with the other being referred to as 'non-Kreutz' or 'sporadic' sungrazers (Meyer, Marsden, and Kracht 1 & 2 families).

Comet C/2011 W3 will probably be the brightest Kreutz-group comet that SOHO has ever observed. It will reach the perihelion on 2011 Dec. 16.02 when it will be it within 880,000 km of the center of the Sun (the comet will pass just 180,000 km from the Sun’s surface).

1. The comet should enter the STEREO/SECCHI HI-1B images on Dec 11, and HI-1A on Dec 12

2. The comet will enter the SOHO/LASCO C3 field of view early on Dec 143. The comet will enter the STEREO/SECCHI COR-2 A & B fields of view early on Dec 15 (UT time), and the COR-1 fields later that day.

We downloaded "Secchi" spacecraft FITS of the Dec. 11 & 12, 2011, and played a little bit with them. Using the image processing algorythms (developed for the CARA collaboration by our fellow collaborator Martino Nicolini). On those images, it's already possible to appreciate a narrow tail, in excess of about 1 deg. Below you can see our renditions (click on the images for a bigger version):

While below you can see an animation showing comet Lovejoy in SECCHI HI-1B on December 11 & 12, 2011 (click on the thumbnail for a bigger version).

According to Dr. Matthew Knight (Lowell Observatory/JHU-APL), Comet Lovejoy was at approximately magnitude 2.0 as on the LASCO C3 images of 16:32UT, Dec 14, 2011). While the peak magnitude is still uncertain, C/2011 W3 could reach the peak brightness at mag -3 or -4 and the comet will probably not survive perihelion. If Comet Lovejoy gets as bright as magnitude -4 or -5, there is a tiny but non-zero chance that it could become visible in the sky next to the sun. But extreme care is needed due to the comet's small solar elongation angle and close proximity to the Sun in the sky.

Below you can see the comet on latest LASCO C3 data available (08:30UT of December 15, 2011). Click on it for a bigger version:

Thanks to Karl, new STEREO-B, SECCHI fits dated back to December 13, 2011 are available. In spite of the fact that the image scale factor is a little small, it's
possible to appreciate the growing of a slight asymmetry of the coma
(toward the north-east):

Below an animation of Dec. 11, 12 and 13 stackings (or click here to see it):

Comet Lovejoy looks to be around mag -1 now and only has ~12hrs left. The comet will reach LASCO C2 around 1500 - 1600UT of today. The animation below shows the comet in the SOHO C3 field (click on the thumbnail for a bigger version):

New STEREO-B, SECCHI fits dated back to December 14, 2011 are available. Below you can see our new image processing on the STEREO/SECCHI HI-1A FITS for Dec 14.5 (click on the image for a bigger version):

In the meantime, new SOHO C3 image dated Dec, 15 at 16:30UT is available (click on the image for a bigger version):

Matthew Knight of the Lowell Observatory and JHU-APL reports on Spaceweather website: "As of 16:30 UT on Dec. 15th, Comet Lovejoy has reached magnitude -3, possibly brighter. It is starting to saturate SOHO images even with narrow filters and shorter than normal exposure times." The comet is now brighter than Jupiter, but not quite as bright as Venus. If these developments continue apace, Comet Lovejoy could become visible to the naked eye in broad daylight before the end of Dec. 15th.

Again: extreme care is needed due to the comet's small solar elongation angle and close proximity to the Sun in the sky. Do not look at or near the sun through unfiltered optics; focused sunlight can seriously damage your eyes.

Comet Lovejoy's perihelion is roughly 5 hours from now, on Dec 16 at 00:30UT. Next SOHO images will be available after 22:20UT.

UPDATE - December 16 at 11UT

Surprisingly as it may seem, comet Lovejoy appears to have survived its close encounter with the sun. Video and images relased by the NASA's Solar Dynamics Observatory (SDO) caught the comet reemerging on the other side of the Sun after its perihelion!!

While in the SDO video below you can see the comet incredibly emerging from perihelion:

Using the images taken from 04:39UT to 10:54UT by the SECCHI outer coronagraph (COR2) on the STEREO Ahead observatory on December 16, we have made this animation clearly showing what is left of the comet nucleus after the close approach with the Sun (at present no one can say how much of the comet's core remains intact). Click on the thumbnail for a bigger version:

Using images taken from SOHO C3 from 15:54 of December 15 to 09:30UT of December 16, we made this animation showing the comet on its course pre and after the perihelion. Click on the thumbnail for a bigger version:

Note how in the last frames the remnant of the pre-perihelion tail is still visible but completely disconnected from the comet:

The missing SOHO C2 post-perihelion fits are now available. We just made this short animation showing the comet C/2011 W3 (Lovejoy) reemerging behind the solar disk after the perihelion on the first hours of December 16, 2011:

As we saw on the previous update, at first the emerging comet was missing its tail. Now on the latest C3 images, it is evident that tails are forming again (with the inclusion of the very narrow tail we saw just before the perihelion, possibly NA or Fe related) and that the comet is still very bright!!

In fact the comet has been succefully observed visually with a 10x50 binoculars by Alexandre Amorim from Brazil on Dec 17.34. He estimated the comet magnitude at -2.9. Here is its report:

While below you can see a groud-based image taken at dawn by Jan Ebr with the FRAM remote telescope (0.3-m SCT) located in Argentina, Malargue:

UPDATE - December 19 at 15UT

Below you can see a beautiful image of the tail of comet C/2011 W3 (Lovejoy) taken on December 19, 2011 by FRAM team (Malargue, Argentina) with 200 mm telephoto lens piggybacked on the main telescope, using also a KAF-1603 camera (from FLI). Click on the image for a bigger version:

UPDATE - December 20 at 13UT

Thanks to Jakub Černý we had the chance to works on the FRAM team fits of December 17, 2011. We sorted and stacked the best V-filtered frames, and have done some image processing on it. Basically, it appears that, apart the two "tail branches", we have an asymmetric coma. In some treatement, there is the hint of a "curved jet" or "shell" (or whatever you would call it) in the inner coma, that appears to originate from the central condensation, developing in a "counterclockwise" direction. Obviously this stuff has to be confirmed in further images, to make sure it's not an artefact of my image processing. You can see below the result (click on the image for a bigger version):

On December 17, 2011 the comet has been imaged in daylight also by amateur astronomer Vincent Jacquesof Breil-sur-Roya, France. Images and video below taken with an 80mm refractor at 80x + near IR filter and camera DMK21 from 09:00 UT to 13:00 UT.

Finally a new image by the FRAM team obtained on December 20, 2011 with a 30-cm Meade SCT F/10 (0.66x) located in Argentina, Malargue.

UPDATE - December 21 at 15UT

The comet has put on a great show for Southern observers. Amateur astronomer Colin Legg has been able to image (with a 5D2 digital camera) the beautiful tail of comet Lovejoy from the Mandurah Estuary on Western Australia around 3:30 WST of December 21, 2011. Below you can see his image and the stunning timelapse of his observing session.

While another observer (Grahame) from Australia took the following image taken on December 21, 2011 at 0400 local time of Perth with canon 7D, 17-85mm lens, ISO 800 F4.5. Click on the image for a bigger version.

UPDATE - December 27 at 14UT

International Space Station Commander Dan Burbank captured spectacular images of Comet C/2011 W3 (Lovejoy) as seen from about 386 Km above the Earth’s horizon on Wednesday, Dec. 21.

(Credit : NASA)

Many beautiful images are arriving from observers in the Southern Hemisphere, you can find a very good selection here & here

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Welcome to our Astronomy blog, devoted in particular to Comets & Asteroids and related topics. This blog is maintained by Italian amateur astronomer Ernesto Guido, particularly active in the study of the small bodies of the Solar System.